the incident that stunned the nation the most, however, happened in newtown, connecticut, when authorities say a gunman descended on a school and killed 20 first graders in addition to half dozen adults, his mother, and himself. >> people responded once they heard about the situation. they responded to come and retrieve their children. when they couldn't find their children, fear set in, panic set in, pain set in. it was fear of the unknown. and when the notification finally had to be made, it was absolutely heartbreaking. >> the incident sparked an immediate and continuing debate over mental health services and gun control. >> the discussion has reemerged as to what we might do not only to deter mass shootings in the future but to reduce the epidemic of gun violence that plagues the country every single day. that conversation needs to continue, but this time, the words need to lead to action. >> down in florida, a single shooting grabbed headlines. teenager trayvon martin was shot and killed in a nighttime encounter with george zimmerman who was part of a neighborhood watch program. debat